Although an iron crawler track has been conventionally used as an endless track traveling device for mobile construction machine vehicles and so on, it has recently come to be used in work on pavement in town areas. Therefore, a link-type rubber crawler track or an integral rubber crawler track is used with the iron crawler track. Here, the link-type rubber crawler track is so constructed that backing shoes having rubber elastic bodies are integrally cured and bound on metallic shoe plates instead of the iron crawler track, or rubber pads having rubber elastic bodies are directly cured and bound on exclusive core metal pieces instead of the metallic shoe plates being mounted on a link comprising a plurality of endlessly-connected track links. Besides, the integral rubber crawler track comprises rubber pad shoes detachable on the metallic shoe plates of the iron crawler track, a tensile strength layer, core metal pieces embedded in an inside circumference of the tensile strength layer at predetermined intervals, and core metal piece guide protrusions for preventing the crawler track from coming off out of the traveling device. The tensile strength layer is so constructed that a plurality of tensile strength materials are arranged and embedded in an endless rubber crawler track main body formed of a rubber elastic body shown in FIG. 13 within a width direction of a rubber crawler track along its circumferential direction to form tensile strength material rows. The core metal piece guide protrusions are formed so as to project toward the inside circumference of the rubber crawler track. Besides, a rubber pad is made in a unit type of a track link length or a continuous type of a length over a plurality of links.
When the conventional rubber crawler track is used in narrow places, on rough ground with many stones, or around a curb in a shoulder of a road, it runs aground on the stones, obstacles, and the curb (FIG. 14A), or is pressed in a lateral direction (FIG. 14B). Therefore, a rubber elastic body put between an end portion of a crawler track width direction in a core metal piece limb embedded in the rubber crawler track and the stones and so on is deformed greatly. Therefore, the rubber elastic body is broken. Whenever such a state is repeated, destruction of the rubber elastic body progresses, thereby finally causing a large crack in the circumferential direction in the rubber crawler track main body.
Some inventions have been proposed to prevent a large crack from occurring in the circumferential direction in the rubber crawler track main body.
For example, an invention for preventing a large crack from occurring in the circumferential direction in the rubber crawler track main body by bending an end portion of a crawler track width direction in a core metal piece limb toward the inside circumference (the ground not-contacting surface) is disclosed in Japanese Patent No. 3077064, Japanese Patent Laid-open Publication Nos. 1999-079015 and 2000-313373. Besides, an invention for preventing a large crack from occurring in the circumferential direction in the rubber crawler track main body by curving an end portion of a crawler track width direction in a core metal piece limb toward the inside circumference (the ground not-contacting surface) is disclosed in Japanese Patent Laid-open Publication No. 1999-268673.
Besides, in Japanese Patent Laid-open Publication No. 1999-105754, an end portion of a crawler track width direction in a core metal piece limb is formed in a round rib configuration to reduce the occurrence of a large crack in the circumferential direction in the rubber crawler track main body.
However, in the above-mentioned inventions, the cost can not be prevented from being raised because a core metal piece molding configuration and processes for making core metal pieces, such as a core metal piece finishing, are complicated in addition to the shape of the core metal piece being complicated.
In addition, in Japanese Utility Model Laid-open publication No. 1977-068532, a reinforcing rib is formed by increasing the thickness of rubber of the ground contacting surface side corresponding to both ends of a crawler track width direction in a core metal piece limb to prevent a large crack from occurring in the circumferential direction in the rubber crawler track main body. Moreover, in Japanese Utility Model Laid-open publication No. 1978-050935, a rubber crawler track has a thick protrusive bar around an end portion of a crawler track width direction in a core metal piece.
However, in the above-mentioned invention, although rubber near the core metal piece limb can be prevented from bending and deforming, rubber outside (the ground contacting surface side) the reinforcing rib or the thick protrusive bar is easy to bend and deform. Accordingly, a large crack in the circumferential direction in the rubber crawler track main body occurs on these portions, and an efficient improvement has not been achieved yet.
Furthermore, in Japanese Patent No. 3077064, to prevent a large crack from occurring in the circumferential direction in the rubber crawler track main body, a cable layer is provided below the ground contacting surface side of a portion of a crawler track width direction of a core metal piece limb, and a synthetic resin material is arranged near the end portion of a crawler track width direction of a core metal piece.
In Japanese Laid-open Publication No. 2000-085642, a low frictional resistive member is embedded in a taper portion of an end of a crawler track width direction in a rubber lug so that the surface is exposed. However, a large crack in the circumferential direction in the rubber crawler track main body cannot be effectively and economically prevented by this method.
The present invention aims to settle the above-mentioned problems and to provide a rubber crawler track capable of preventing a large crack from occurring in the circumferential direction in the rubber crawler track main body effectively and economically.